The present invention generally relates to a solid catalyst composition and a process for preparing the solid catalyst. Furthermore, the present invention provides for a polyurethane catalyst which maintains its activity in the presence of silica or silica-treated fillers.
In the field of urethane chemistry many variables exist to modify or enchance the physical characteristics of a polyurethane composition. The type of catalyst employed is one such variable. The catalyst can vary the reaction rate of the isocyanate group to provide different branching, crosslinking and chain extension. The reaction rate itself is also important as, for example, in reaction injection molding (RIM) where a fast cure rate is necessary.
Another important variable in a polyurethane composition is the filler. Fillers provide reinforcement, tensile strength, compression set and shrink resistance to the compound. They also increase the compound's volume which has the economic incentive of lowering cost. Various fillers useful in urethane compositions are taught in U.S. Pat. Nos. 3,441,523 and 3,150,109. Those fillers known to be particularly useful in polyurethane systems include silica, milled glass fibers, wollastonite and carbon black.
Silica is especially useful as a reinforcing filler because it does not interfere with the color imparted by a pigment added to the composition. Where no pigments are employed a silica filler will yield a light colored final product suitable for painting. One disadvantage, however, is that the free silanol groups present on silica and silica-treated fillers deactivate urethane catalysts to result in long cure times or complete deactivation. This is especially a problem when short cures are necessary as in reactive injection molding (RIM) processes where fillers, such as silica, are employed. A dilemma is thus created. To reduce the filler content would change the physical properties and increase the stock's cost, while to accept a longer cure rate would make injection molding very difficult. It, therefore, would be advantageous to create a catalyst which would not be deactivated when added to a polyurethane composition which contains a silica or silica-treated filler.
A catalyst insensitive to free silanols would be especially valuable in the area of polyurethane RIM manufacture.
Polyurethane RIM already plays a significant role in the automobile industry with applications in front and rear fascia, bumpers, and many interior applications. Silica fillers can be advantageously employed in this area; however, in the automotive applications area, the use of polyurethane RIM for exterior body applications or in other large part applications require a resistance to heat sag along with an ability to manufacture at high production rates, which means relatively fast cure rates. Therefore, a catalyst which is not deactivated by the silica or silica-treated fillers is critical.